The present invention relates to a digital input class-D amplifier suitable for use as a power amplifier of audio equipment.
The class-D amplifier is an amplifier which generates a pulse train subjected to pulse-width modulation or pulse-density modulation in accordance with an input signal and which drives a load by means of the pulse train. The class-D amplifier is often used as a power amplifier which drives a speaker in audio equipment or the like. The class-D amplifier is for causing an electric current to flow to a load by means of switching operation without causing a d.c. bias current to flow into an output transistor connected directly to the load. Hence, the class-D amplifier has an advantage of little wasteful power being consumed by an output transistor and the ability to drive the load with high efficiency.
[Patent Document 1] JP-A-1-204527
[Patent Document 2] JP-A-2006-304084
[Patent Document 3] JP-A-2001-85998
Incidentally, in the class-D amplifier, a modulation signal used for pulse-width modulation, or the like, must be an analogue signal. Therefore, when a signal, an object of reproduction, which is acquired from a sound source or the like is a digital signal, the digital signal must be converted into an analogue signal or a bit stream (e.g., a bit stream acquired through ΔΣ) which can be regarded being identical with an analogue signal, and the analogue signal or the bit stream must be supplied to the class-D amplifier. When there is adopted a configuration of subjecting a digital signal to digital-to-analogue conversion and supplying an analogue signal to the class-D amplifier, there is a problem of playback quality, or the like, being affected by an error arising at the time of digital-to-analogue conversion.